Method and apparatus for waste stream recovery

1. A method for recovering a product mixture from a diaryl carbonate manufacturing waste stream comprising;

reacting said waste stream with an alkyl alcohol to form a reaction mixture comprising said product mixture and at least one waste component; and

separating said product mixture from said reaction mixture.

2. The method according to claim 1 wherein said reaction occurs in liquid phase or a combination of liquid and vapor phase.

3. The method according to claim 1 wherein said reaction occurs in a batch or a continuous mode.

4. The method according to claim 1 wherein said reaction occurs at a temperature of about 80to about 250° C.

5. The method according to claim 1 wherein said reaction occurs at a temperature of about 140to about 180° C.

6. The method according to claim 1 wherein maid reaction is carried out at a pressure of about atmospheric pressure to about 5,000,000 Pascal.

7. The method according to claim 1 wherein said reaction is carried out at a pressure of about 500,000 to about 2,000,000 Pascal.

8. The method according to claim 1 wherein the weight ratio of said alkyl alcohol to said waste stream is maintained at about 0.05 to about 100.

9. The method according to claim 1 wherein the weight ratio of said alkyl alcohol to said waste stream is maintained at about 0.2 to about 1.5.

10. The method according to claim 1 wherein said waste stream comprises transesterification catalyst, diaryl carbonate, aromatic salicylate and polycarbonate oligomers and said product mixture comprises a dialkyl carbonate, aromatic alcohol, alkyl salicylate and said alkyl alcohol.

11. The method according to claim 10 wherein the concentration of said transesterification catalyst is at about 0.0001% to about 10% by weight relative to said waste stream.

12. The method according to claim 10 wherein the concentration of said transesterification catalyst is at about 0.1% to about 10% by weight relative to said waste stream.

13. The method according to claim 10 wherein the concentration of said transesterification catalyst is at about 1% to about 4% by weight relative to said waste.

14. The method according to claim 1 wherein after separation of said product mixture, the waste component is disposed of.

15. The method according to claim 1 wherein said waste stream further comprises a first waste stream and a second waste stream.

16. The method according to claim 15 wherein said first waste stream comprises said transesterification catalyst, said diaryl carbonate and said aromatic salicylate and said second waste stream comprises said diaryl carbonate, polycarbonate oligomers, aromatic salicylate and transesterification catalyst.

17. The method according to claim 1 wherein said waste stream and said alkyl alcohol is mixed before reacting.

18. The method according to claim 17 wherein said waste stream and said alkyl alcohol is mixed in an online mixer or a mixing vessel.

19. The method according to claim 1 wherein a mixture of said alkyl alcohol and said dialkyl carbonate is used to react with said waste stream and the concentration of said alkyl alcohol in said mixture is about 1% to about 99% by weight.

20. A method for recovering a product mixture from a waste stream in a diaryl carbonate manufacturing process comprising:

introducing reactant streams comprising a dialkyl carbonate, an aromatic alcohol and a transesterification catalyst to a first reactive distillation column;

recovering from said first reactive distillation column a first top stream comprising said dialkyl carbonate, an alkyl alcohol, an alkyl aryl ether and said aromatic alcohol and a first bottom stream comprising an alkyl aryl carbonate, said transesterification catalyst, diaryl carbonate and an aromatic salicylate;

introducing said first bottom stream into a second reactive distillation column to produce a diaryl carbonate;

recovering from said second reactive distillation column a first side stream comprising said dialkyl carbonate, aromatic alcohol, alkyl aryl ether and a second bottom stream comprising said diaryl carbonate, alkyl aryl carbonate, transesterification catalyst, aromatic salicylate and dialkyl carbonate;

introducing said first side stream into a second rectification column to separate a dialkyl carbonate stream from said alkyl aryl ether and said aromatic alcohol, and recycling said dialkyl carbonate stream to a first rectification column;

introducing said second bottom stream to a third reactive distillation column;

recovering from said third reactive distillation column a second top stream comprising unreacted said aromatic alcohol, dialkyl carbonate and alkyl aryl ether and recycling said second top stream to said first reactive distillation column;

introducing said first top stream into said first rectification column;

recovering from said first rectification column a first azeotrope top stream comprising said dialkyl carbonate/alkyl alcohol azeotrope, and a third bottom stream comprising said dialkyl carbonate, aromatic alcohol and alkyl aryl ether and recycling said third bottom stream to said first reactive distillation column;

recovering a fourth bottom stream comprising said diaryl carbonate from the bottom of said third reactive distillation column and introducing said fourth bottom stream into a first evaporator;

recovering ftom said first evaporator a third top stream comprising said diaryl carbonate, alkyl aryl carbonate, aromatic alcohol, an alkyl salicylate and an aromatic salicylate and a fifth bottom stream comprising said diaryl carbonate, aromatic salicylate and transesterification catalyst and introducing said fifth bottom stream into a second evaporator;

recovering from said second evaporator a fourth top stream comprising said diaryl carbonate and a sixth bottom stream comprising said transesterification catalyst, said diaryl carbonate and said aromatic salicylate;

splitting said sixth bottom stream into a first recycle stream and a first bottom waste stream and recycling said first recycle stream into said first reactive distillation column;

introducing said third top stream and said fourth top stream into a third rectification column;

recovering from said third rectification column a fifth top stream comprising said alkyl aryl carbonate and aromatic alcohol and a seventh bottom stream comprising said diaryl carbonate, polycarbonate oligomers, said aromatic salicylate and said transesterification catalyst;

introducing said fifth top stream to said third reactive distillation column and introducing said seventh bottom stream into a fourth rectification column;

recovering from said fourth rectification column a sixth top stream comprising said diaryl carbonate and a second bottom waste stream comprising said diaryl carbonate, polycarbonate oligomers, aromatic salicylate arid transesterification catalyst;

introducing sald second bottom waste stream, said first bottom waste stream and said alkyl alcohol into a mixing unit to produce said waste stream;

introducing said waste stream into one or more reactors;

reacting said waste stream with said alkyl alcohol to form a reaction mixture;

introducing said reaction mixture into a separating unit;

recovering from said separation unit a product mixture and an eighth bottom stream comprising a bisphenol, said transesterification catalyst and unreacted waste;

recycling said product mixture into said third rectification column; and

introducing said eighth bottom stream into a disposal unit, wherein said product mixture comprises a dialkyl carbonate, an aromatic alcohol and said alkyl alcohol; said waste stream comprises a transesterification catalyst, said diaryl carbonate, an aromatic salicylate and polycarbonate oligomers; and said reaction mixture comprises said dialkyl carbonate, said aromatic alcohol, said alkyl alcohol, a bisphenol, an alkyl salicylate, and unreacted waste.

21. The method according to claim 20 wherein said alkyl alcohol is introduced directly to said reactor.

22. The method according to claim 20 wherein part of said first azeotrope top stream is used to react with said waste stream.

23. The method according to claim 22 wherein part of said first azeotrope stream is introduced to said mixing unit.

24. The method according to claim 22 wherein part of said azeotrope stream is sent directly to said reactor.

25. The method according to claim 20 wherein said first bottom waste stream and said second waste stream are introduced directly into said reactor.

26. The method according to claim 20 wherein said reactor is selected from the group consisting continously stirred tank reactor, plug flow reactor and bubble column reactor.

27. The method according to claim 20 wherein said reactor is a combination of a continuously stirred tank reactor, a plug flow reactor and a bubble column reactor.

28. The method according to claim 20 wherein residence time in said reactor is up to about 120 minutes.

29. The method according to claim 20 wherein said separation unit is selected from the group consisting flash drum, distillation column and evaporator.

30. The method according to claun 29 wherein said separation unit is a distillation column.

31. The method according to claim 30 wherein said distillation column is maintained at a temperature of about 100 to about 220° C.

32. The method according to claim 30 wherein said distillation column is maintained at a pressure of about 100 Pascal to about 500,000 Pascal.

33. The method according to claim 30 wherein said distillation column is maintained at a pressure of about 100 to about 30,000 Pascal.

34. The method according to claim 29 wherein said separation unit is a flash drum.

35. The method according to claim 34 wherein said flash drum is maintained at a temperature of about 140 to about 220° C.

36. The method according to claim 34 wherein said flash drum is maintained at a pressure of about 100 Pascal to about 500,000 Pascal.

37. The method according to claim 34 wherein said flash drum is maintained at a pressure of about 100 to about 30,000 Pascal.

38. The method according to claim 20 wherein said product mixture is recycled back to a column selected from the group of columns consisting said first, second and third reactive distillation column and first and third rectification column.

39. The method according to claim 20 wherein said eighth bottom stream is further purified to recover said bisphenol.

40. The method according to claim 39 wherein said recovered bisphenol is recycled to polycarbonate polymerization process.

41. The method according to claim 20 wherein said disposal unit is a burner.

42. The method according to claim 20 wherein maid product mixture further comprises an alkyl salicylate.

43. The method according to claim 42 wherein said product mixture is further purified to recover said alkyl salicylate.